Various types of capacitive accelerometer have been proposed and commercialized, see for example Yazdi et al., “Micromachined Inertial Sensors”, Proc. IEEE, Vol. 86, pp. 1640–1659 (1998). However, many conventional sensors for vertical acceleration detection comprise two facing electrodes, requiring a wafer bonding process. See for example Spangler and Kemp, “ISAAC-Integrated Silicon Automotive Accelerometer”, Proc. Transducers'95, pp. 585–588 (1995); and Suzuki et al., “A 1024-Element High-Performance Silicon Tactile Imager”, Trans. Electron Devices, Vol. 37, pp. 1852–1860 (1990).
An example of such a conventional accelerometer architecture including facing electrodes is shown in FIG. 1(a). Conventional accelerometer device 100 comprises seismic mass 102 supported by support beams 104 over substrate 106. The underside of seismic mass 102 bears a first electrode 108, and the surface of substrate 106 bears second electrode 110. Acceleration in the z-direction is indicated by a change in position of seismic mass 102 relative to substrate, and specifically by a change in the capacitance exhibited by the capacitor comprising plates 108 and 110 separated by gap 112.
Devices for detecting lateral acceleration typically comprise high-aspect ratio beams and comb fingers fabricated by deep reactive ion etching (DRIE) techniques, for example as shown at http://www.analog.com/technology/mems/accelerometers.
While the above-referenced conventional accelerometer devices are effective, improved accelerometer devices and techniques for manufacturing such improved accelerometer devices are highly desirable.